Mounting Your Motor to an Electric Actuator with Tolomatic

Many industrial manufacturers choose to install a 3rd party motor onto their Tolomatic electric actuator. If you choose this option, you’ll first be faced with the many different types of motors (servo, stepper, induction) available on the market, and how each selection can affect the mechanical design (mounting and coupling) of the actuator. Motors are chosen based on different categories, such as ease of use, brand, availability, performance, package and size. We’re taking a look at the advantages of both the inline and the reverse parallel motor mounting designs for electric actuators to help inform your decision and avoid common mounting mistakes.

Choosing a mount design

Inline Mount

Inline motor mounts allow the user to directly mount the motor in line with the driveshaft of the actuator. This design requires fewer components to couple the motor to the actuator, and the direct coupling allows the actuator to perform more accurately with the reduced backlash compared to the belt and pulley system of a reverse parallel motor kit. Inline motor mounts also take up less space in the width and height of the actuator solution, but will make the overall length much longer. The inline motor mount also limits the number of rear pivot mounting options, such as a rear clevis.

Inside an inline motor mount is a coupler that links the motor to the actuator’s driveshaft. The most common types of couplers used are spider, servo or rigid (fixed). Deciding which type to use typically depends on the application requirements:

  • Spider Coupler: A standard spider coupler utilizes two coupler halves with jaws that engage a rubber “spider” material between the two halves. This design is easy to manufacture, economical, and allows for some alignment correction to occur between the motor’s shaft and the actuator’s driveshaft to compensate for any misalignment. (CLICK HERE to see spider coupler mounting in action.)
  • Servo Couplers: Another popular design is the “Servo Style” coupler. This design aims to combine advantages of both rigid and spider coupler styles. Serve couplers consist of an aluminum material with mid sections machined to allow for some flex to occur in the absence of a rubber spider material. This style is typically more expensive than a spider coupler due to its mechanical complexity.
  • Fixed Couplers: The “fixed” coupler is typically used where application parameters call for zero backlash or extremely high torque applications. Unlike the other couplers, this style is less common because it is the most difficult to implement correctly. A “fixed” design requires that there be no misalignment between the actuator and motor shaft. If the two shafts are out of alignment, it could side load either shaft. During normal operation, this misalignment could result in shaft fatigue and damage to the motor/actuator bearing system, resulting in permanent damage. Care must be taken when using a fixed coupler to ensure system alignment. (Check out a fixed coupler design HERE.)

Reverse Parallel (RP) Mounts

Another option for motor mount design is the reverse parallel motor mount design. In this design, the motor is mounted parallel to the actuator and coupled to the actuator drive shaft through belts/pulleys or gears. This type of motor mounting allows for both rear trunnion and rear clevis pivot mounts, increasing mounting flexibility. (See a reverse parallel mount design HERE.)

The belt material used in the reverse parallel design will have some amount of compliance, which can result in slightly higher amounts of backlash and lower repeatability when compared to an inline design. Backlash will affect the overall precision of the system.

Mounting Tips

Inline Motor Mounting

With so many different motor designs to choose from, mounting a pulley on the motor’s shaft can require special couplers. Some common coupling techniques include collar clamps, trantorque, or set screw designs.

A collar clamp is a popular design due to the ease of installation. A trantorque is more complex and requires a working knowledge of how they are constructed to avoid installation challenges.

A trantorque consists of a cylinder shape body with a hole through the center and a hex head provided on one end. When installing a trantorque bushing, the motor’s shaft is slid into the bushing and the motor pulley is slid over the bushing. To keep the motor shaft from spinning, it needs to be held in place while turning the hex pattern with a wrench to allow the trantorque bushing to grab onto the motor’s shaft and tighten itself to the motor pulley. A torque spec from the manufacturer should be referenced during installation.

RP Orientation Mounting

Mounting a motor on a reverse parallel motor mount which utilizes a belt and pulley design can require more attention compared to the simplicity of the inline design. While tensioning the belt, attention must be paid to the process to avoid over or under tensioning the belt. Belts that are under-tensioned will cause the belt’s teeth to cog (skip teeth). Belts that are over-tensioned will cause the belt to side load the motor shaft and the actuator’s driveshaft.

Several motor mount styles are available in actuator solutions. Depending on the application, torque, and mounting requirements, a reverse parallel or inline mounting configuration may be recommended. Care should be taken when sizing an actuator to ensure that the optimal mounting, design style, and belt reduction ratio is selected. Additionally, special attention should be taken during the motor mounting procedure to ensure alignment and proper belt tension is applied to optimize the overall life of the actuator.

This information in the article was originally published in Tolomatic’s ebook Mounting Your Motor to an Electric Actuator.

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